IN-SITU TECHNIQUE FOR MEASURING THE RESISTIVITY OF LITHIUM INTERCALATION COMPOUNDS AS A FUNCTION OF LITHIUM COMPOSITION

An automated dc method has been developed to allow resistivity measurements of thin film electrodes of electrochemical intercalation cells to be made in situ, as the cell charges and discharges. High precision current sources and voltmeters are used both to charge/discharge the cell and to measure electrode resistance. The measured resistance will be simply that of the electrode when its resistivity is small, but when electrode resistivity is large compared to the ionic impedance of the electrolyte, the transport of Li+ ions in the electrolyte provides an alternate current path. In order to interpret the resistance data in the latter case we have developed an equivalent circuit model that includes both electronic and ionic current paths. This method can, in principle, be used to measure the dependence of electrode resistivity on intercalant concentration for any material which can be made into a thin film electrode.